Drop on demand inkjet technology has been employed in commercial products such as printers, plotters, and facsimile machines. Generally, an inkjet image is formed by the selective activation of inkjets within a print head to eject ink onto an ink receiving member. For example, an ink receiving member rotates opposite a print head assembly as the inkjets in the print head are selectively activated. The ink receiving member may be an intermediate image member, such as an image drum or belt, or a print medium, such as paper. An image formed on an intermediate image member is subsequently transferred to a print medium, such as a sheet of paper.
FIGS. 5A and 5B illustrate one example of a single inkjet ejector 10 that is suitable for use in an inkjet array of a print head. The inkjet ejector 10 has a body 48 that is coupled to an ink manifold 12 through which ink is delivered to multiple inkjet bodies. The body also includes an ink drop-forming orifice or nozzle 14 through which ink is ejected. In general, the inkjet print head includes an array of closely spaced inkjet ejectors 10 that eject drops of ink onto an image receiving member (not shown), such as a sheet of paper or an intermediate member.
Ink flows from the manifold to nozzle in a continuous path. Ink leaves the manifold 12 and travels through a port 16, an inlet 18, and a pressure chamber opening 20 into the body 22, which is sometimes called an ink pressure chamber. Ink pressure chamber 22 is bounded on one side by a flexible diaphragm 30. A piezoelectric transducer 32 is secured to diaphragm 30 by any suitable technique and overlays ink pressure chamber 22. Metal film layers 34, to which an electronic transducer driver 36 can be electrically connected, can be positioned on either side of piezoelectric transducer 32.
Ejection of an ink droplet is commenced with a firing signal. The firing signal is applied across metal film layers 34 to excite the piezoelectric transducer 32, which causes the transducer to bend. Because the transducer is rigidly secured to the diaphragm 30, the diaphragm 30 deforms to urge ink from the ink pressure chamber 22 through the outlet port 24, outlet channel 28, and nozzle 14. The expelled ink forms a drop of ink that lands onto an image receiving member. Refill of ink pressure chamber 22 following the ejection of an ink drop is augmented by reverse bending of piezoelectric transducer 32 and the concomitant movement of diaphragm 30 that draws ink from manifold 12 into pressure chamber 22.
To facilitate manufacture of an inkjet array print head, an array of inkjet ejectors 10 can be formed from multiple laminated plates or sheets. These sheets are configured with a plurality of pressure chambers, outlets, and apertures and then stacked in a superimposed relationship. Referring once again to FIGS. 5A and 5B for construction of a single inkjet ejector, these sheets or plates include a diaphragm plate 40, an inkjet body plate 42, an inlet plate 46, an outlet plate 54, and an aperture plate 56. The piezoelectric-transducer 32 is bonded to diaphragm 30, which is a region of the diaphragm plate 40 that overlies ink pressure chamber 22. In previously known inkjet ejectors, these plates are metal plates that are brazed to one another with gold.
In some known thermal inkjet print heads, the aperture plate may be a polymer layer in which apertures are formed using laser ablation. The advantages of using a polymer layer include low cost and the ability to taper or otherwise shape the apertures. Using a polymer layer also presents challenges to print head design. In the present art, the outlet plate is generally manufactured from a metal layer, such as stainless steel. The metal layer is etched with openings that fluidly couple the apertures in the polymer aperture plate to a pressure chamber in a body layer once the print head assembly is completed. An adhesive is used to bond the polymer aperture plate to the outlet plate. The adhesive bond is formed with heat and pressure once the two plates are positioned adjacent to one another. Since the apertures in the polymer aperture plate are smaller than the openings in the outlet plate, solid portions of the polymer aperture plate extend over the openings in the outlet plate. The attendant lack of support for these portions as the metallic outlet plate is pressed against the polymer aperture plate produces uneven pressure on the polymer aperture plate and causes the polymer aperture plate to warp. While an ideal print head is usually configured to eject ink droplets perpendicularly to the aperture plate's surface, the warped apertures may eject droplets at different angles, reducing print quality.
The lack of flatness in the aperture plate arising from the application of uneven pressure to polymer layers is known to the art. U.S. Pat. No. 5,467,115 discloses the cutting of extra trenches in the silicon die mounting material to produce unsupported areas of the aperture plate that are symmetrical with regard to the apertures in the polymer aperture layer. These symmetrical unsupported areas help reduce errors in apertures caused by the polymer layer warping. While this method tries to reduce the negative effects caused by warped nozzles, it does not address the underlying problem that the polymer aperture plate is being warped during the print head fabrication process. Additionally, existing thermal inkjet print heads in which the above described compensation method addresses effects at the ends of the plates and not the effects at each aperture. A print head fabrication method for making print heads with flat polymer aperture plates benefits the print head fabrication field.